The present invention relates to a sheet delivery mechanism of a front access type image forming apparatus which allows user access to an internal space of the apparatus from the front thereof.
When multiple copies of an original document are printed by a conventional image forming apparatus, it is usually difficult for a user to discern boundaries between the individual copies of printed sheets (such as a boundary between a last page of a first copy and a first page of a second copy) discharged onto a sheet delivery tray and, therefore, the user is forced to undertake a tedious sorting task of manually separating the individual copies from one another.
To overcome this inconvenience, the prior art proposes various kinds of sheet delivery mechanisms featuring a shifter function which enables a user to distinctly discern boundaries between multiple copies (prints) of a multiple-page document. Arrangements for realizing the shifter function are roughly divided into three types.
(a) A first arrangement is to feed printing paper in different orientations (portrait and landscape) and rotate printed images clockwise and counterclockwise by 90 degrees for every other copy of a document as proposed in Japanese Laid-open Patent Publication No. 1999-199124, for example.
(b) A second arrangement is to use a movable sheet delivery tray (offset tray) which is shifted (offset) to different positions when receiving multiple copies of printed sheets ejected from a fixed sheet output position as proposed in Japanese Laid-open Patent Publication No. 2000-86056, for example.
(c) A third arrangement is to vary the sheet delivery position by shifting (offsetting) printed sheets being discharged by sheet output rollers provided in a sheet delivery section as proposed in Japanese Laid-open Patent Publication Nos. 1993-186121 and 1996-208091, for example.
Recently proposed to meet a growing demand for compact design are front access type image forming apparatuses which allow user access to an internal space of the apparatus from the front thereof. Many of this type of image forming apparatuses are designed such that an image scanning section is located at an upper part of the apparatus, a sheet feeding section is located at a lower part of the apparatus, and an image forming section is disposed between the image scanning section and the sheet feeding section at one side of the apparatus, in which the image scanning section, the image forming section and the sheet feeding section are arranged generally in a U shape in front view.
To meet also an increasing demand for advanced features, the front access type image forming apparatus incorporates a duplex (double-sided) image-forming function which is realized by a switchback paper transfer method instead of a normally used intermediate tray method. In the switchback paper transfer method, a sheet of paper is reversed by transferring the sheet in a direction opposite to an ordinary sheet transport direction immediately after an image has been formed on one side of the sheet.
For the front access type image forming apparatus, it is not desirable to employ the aforementioned first arrangement (a) of Japanese Laid-open Patent Publication No. 1999-199124. This is because it is necessary to provide multiple paper cassettes for each paper size to feed the printing paper in different orientations and this makes it difficult to achieve compactness of the apparatus. The aforementioned second arrangement (b) of Japanese Laid-open Patent Publication No. 2000-86056 is not desirable for the front access type image forming apparatus either, because it is difficult to accommodate the offset tray in a limited space available in a central empty space of a generally U-shaped structure (in cross section) of the apparatus.
In contrast, the aforementioned third arrangement (c) proposed in Japanese Laid-open Patent Publication Nos. 1993-186121 and 1996-208091, in which the printed sheets discharged by the sheet output rollers provided in the sheet delivery section are offset to shift the sheet delivery position, seems to be suited to the front access type image forming apparatus since its sheet delivery tray need not be moved like the offset tray without causing much hindrance to compact design.
When this third arrangement is employed, however, the user who gains access to the sheet delivery tray from the front of the apparatus can not visually watch the whole area of the sheet delivery tray, because the sheet delivery tray is located in a central empty space of the apparatus. Therefore, when removing sorted copies of printed sheets from the sheet delivery tray, the user may grasp an improper part of the printed sheets, inadvertently mixing up the already sorted copies.